OPLxLPT adapter for ST/TT/F030

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nokturnal
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Joined: Wed Aug 12, 2020 12:30 pm

OPLxLPT adapter for ST/TT/F030

Post by nokturnal » Tue May 04, 2021 8:47 pm

Hi,
Some time ago I started a small project to connect opl2/3lpt to Atari ST/f030. From pcb it looks like it started it last year :? .
In general I've rewired pins a little and created two test boards (with and without diodes (one version for easier debugging of Centronics/Printer port), second one for standard user). I'm not electronics expert, so sorry if anyone sees something very offensive. This is the very first PCB in my life, so probably isn't the best in the world. I've tried my best to not kill both opl3lpt and Atari (values of resistors are from ceiling on schema, so see photos for actual value, I use one type).

Wiring looks like this:

Code: Select all

OPLxLPT    CENTRONICS                    F030        ST
     1: A0       ->  /Strobe   CTRL-0   1 /STROBE   1 /STROBE
     2: D0      <->  Data0              2 /DATA0    2 /DATA0
     3: D1      <->  Data1              3 /DATA1    3 /DATA1
     4: D2      <->  Data2              4 /DATA2    4 /DATA2
     5: D3      <->  Data3              5 /DATA3    5 /DATA3
     6: D4      <->  Data4              6 /DATA4    6 /DATA4
     7: D5      <->  Data5              7 /DATA5    7 /DATA5
     8: D6      <->  Data6              8 /DATA6    8 /DATA6
     9: D7      <->  Data7              9 /DATA7    9 /DATA7
    14: /RD      ->  /Linefeed CTRL-1   +5V         +5V
    16: /WR      ->  Init      CTRL-2   11 /BUSY    11 /BUSY
    17: A1       ->  /Select   CTRL-3   17          GND             (OPL3LPT only)
Schema looks like this:

end-user version

opl3lptAdapterSchema2_800.png
opl3lpt adapter schema prototype end user
opl3lptAdapterSchema2_800.png (147.23 KiB) Viewed 187 times

development

opl3lptAdapterSchema_800px.png
opl3lpt adapter schema prototype development
opl3lptAdapterSchema_800px.png (150.7 KiB) Viewed 187 times
Real thing like this (it's not final, because I will make it more condensed and nicer to connect):

pcb_opl3lpt_pcb.png
pcb_opl3lpt_pcb.png (1.85 MiB) Viewed 187 times

Problems:
I've got an issue with dev adapter and diodes. OPL3LPT is powered up from usb adapter and I stole 5v from pin 1 of usb port and wired it via resistor to pin 14 on OPLxLPT side, so it is in high state all the time (connected via resistor just to be safe).

When usb power is connected on opl3lpt side:
With connected D1 diode it light s up and is bright, but all other diodes don't light up at all.
With removed D1 diode. All diodes begun to turn on/off according to signal from lpt port(as expected), but are very dimmed (like current was really low and blue diodes, which are more power hungry don't lit at all - my test program which turns on/off data lines lits every diode beside blue ones).

With usb power is disconnected on opl3lpt side:
Everything works as expected, but d1 isn't lit, because it isn't powered up from pin 14. Diodes are bright.

Here is without usb power (state on f030 boot, /strobe and /busy set to high):

diodesIssue_002.png
diodesIssue_002.png (733.81 KiB) Viewed 187 times

Here is with usb power (state on f030 boot, /strobe and /busy set to high):

diodesIssue_001.jpeg
dev board usb connected
diodesIssue_001.jpeg (173.76 KiB) Viewed 187 times

So, I've got several questions here.
1) Anyone more electrically competent could tell me what I'm doing wrong here and how to fix those issues with dimmed leds?
2) Data lines / signals are not suitable for powering diodes (bare wires), how I could protect them (psg and computer) better when attaching diodes? I imagine resistors aren't good enough.
3) There is no possibility to switch opl3lpt to read state right now, there is not enough signals on Atari side. Maybe anyone has suggestions how to overcome this? But it isn't very relevant, just nice thing to have.

Shortcomings:
Only f030 can enable opl3 features, because Select In line can be set to low/high. On ST there is no possibility to enable opl3 features right now.

Any suggestions welcome, still working on test programs/drivers for it. Unfortunately I haven't managed to produce any sound with it yet, so it's still work in progress (I've adapted sample tune replay by Daniel Illgen targeted for cartridge port, but still it isn't working as expected with this adapter, probably bad timings and/or still something hardware related I'm not sure).

Here are some better pics of adapters and opl3lpt with mods I mentioned above:

opl3lpt_mod.jpeg
modded opl3lpt
opl3lpt_mod.jpeg (102.82 KiB) Viewed 176 times
adapters_opl3lpt.jpeg
adapters assembled
adapters_opl3lpt.jpeg (123.82 KiB) Viewed 176 times
saulot/[nokturnal]
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exxos
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Re: OPLxLPT adapter for ST/TT/F030

Post by exxos » Tue May 04, 2021 8:59 pm

I have only had a quick read but one thing to note about LED's, is if you are connecting them to a actual signal, then the LED can clamp it to basically a continuous logic low level.. You should always buffer them...

Similar if you are trying to light up LEDs on particular signals in series you can end up with a voltage drop .. where it will no longer register a logic high..
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viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?

nokturnal
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Joined: Wed Aug 12, 2020 12:30 pm

Re: OPLxLPT adapter for ST/TT/F030

Post by nokturnal » Tue May 04, 2021 9:08 pm

Yes, I thought about it and heard about term "buffering". But, I don't know how to do it, I'm not electrical engineering guy (not yet 8-) ).
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Re: OPLxLPT adapter for ST/TT/F030

Post by exxos » Tue May 04, 2021 9:13 pm

nokturnal wrote:
Tue May 04, 2021 9:08 pm
Yes, I thought about it and heard about term "buffering". But, I don't know how to do it, I'm not electrical engineering guy (not yet 8-) ).
use something like a 74LS244.. drive the LEDS from that and not direct from your signals.
https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxoshost.co.uk/atari/store2/ - All my hardware mods for sale - Please help support by making a purchase.
viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?

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